An endoprosthesis with these features as sub-features is known from DE 36 29 799 A1. Described therein are two connecting elements joined by means of pegs with corresponding receiving seats on the main body, whereby one of the connecting elements--as mentioned--is used for producing a connection of the main body with the ilium region of the remaining pelvis, while the other connecting element serves for joining the main body with the pubic bone region of the remaining pelvis. The actual fixing of the connecting elements to the remaining bone is carried out by means of plate parts that are brought into position against the bone parts and that have holes through which bone screws are screwed transversely through the remaining bone.
Admittedly, newer diagnostic procedures permit the detection of tumors by means of computer tomography and the simulation in plastic of the bone regions as well as the regions stricken by the tumor. With the help of these models, surgeons can then determine before the actual operation how the implant ultimately must look, which resections must be carried out ahead of time, and how the individual procedures must be done during the operation. These preparatory measures are indeed very helpful, but do not guarantee a smooth operative procedure. It is felt to be particularly disadvantageous in the case of the known endoprosthesis that it is too inflexible.
Thus, during massive operations, in the course of which parts of the entire pelvis, including the natural joint socket, are resected, it can very easily happen that the bone screws are screwed into the bones at places that are at first thought to be correct, whereas it can turn out after the assembly of the modular prosthesis that a positioning correction is urgently needed. In this case, the bone screws must then be at least partly removed, one or the other of the connecting elements must be placed into a different position, and the bone screws screwed back into the bones that are in any case weakened by the resection, while leaving behind through the bones holes from the first attempt which are now no longer necessary.
In addition to that, a swivelling of the main body around the one peg of the first connecting element is certainly possible before the so-called fixed site between the first connecting element and the main body has been established. In any event, if in the case of the known endoprosthesis the main body swivels around the axis of the peg, then the main body is rotated out of the anatomically determined plane of a natural hip joint socket, so that in some cases it is possible for the artificial hip joint to come to rest at a different height than the natural hip joint which is left in the patient's body on the other side of the pelvis. The consequences of this are possible excessive loads on the remaining bone, from which significant postoperative complications can result.
An additional endoprosthesis for the replacement of a human pelvis part has become known from DE-41 33 433 C1. In comparison with the endoprosthesis from the above-mentioned reference, the endoprosthesis described in this document has a greater degree of freedom in its adjustability. It consists of an outer shell, whose wall is penetrated by a large number of holes bored through it. A screw is set through one of these bored holes in order to be screwed together with a conical peg that is formed on a connecting element for the ilium stump. An intermediate piece between the peg and the outer shell acts as a spacer. The selection of the hole through which the screw is placed is to be made by the surgeon during the operation, so that a replacement positioning of the outer shell in relation to the remaining pelvis parts can be made. Thereafter, the outer shell is joined with the ilium stump by means of additional connecting pieces.
Quite apart from the fact that the metal outer shell is significantly weakened mechanically by the large number of holes bored through it, it also has to be considered disadvantageous that the surgeon must concern himself with a large number of small parts during the operation, until the endoprosthesis attains a replacement positioning. This large number of elements must be reset with every change of the installed position.